Yamaha C85 overheating

[Tommy in FLL]

Hi-

I pulled the thermostat cover off of my '96 Yamaha C85 today. This engine runs without a thermostat, due to some internal problem that causes it to overheat. The warning siren goes off if I run the engine at 3000 rpm [planing speed] for more than about one minute.

I live in Fort Lauderdale, and the canal behind my house and all the canals that I normally operate in are "no wake". They are also all filled with brackish water, which is largely salty.

-Last night I was feeling good. I took the boat about a half-mile from my house, cleared the canals of manatees....and then brought it up on plane. I normally never do this, since it is illegal, but I wanted to see what would happen and the sea cows are out in the intercoastal anyway. It ran good for 60 seconds, and I was 200 yards away from the house when the overheat horn came on. I pulled it back to wake speed, shut it down, and 30 seconds later when I fired it up again the horn was off.

Today I pulled the thermostat cover. I removed the cover, removed the pressure regulator and its' spring, and used a screwdriver to remove a bunch of spooge from the engine.

Is there any other word for this stuff?

This stuff is kind of "clear". What is it, and is there a product I can pour down the water channels to burn this stuff out?

THE BIG PROBLEM: A bunch of crud in the cooling passages. But I'm not sure that it is actually a problem~

I pulled the thermostat cover off to test a hypothesis that I've had for a while: the exhaust gaskets are leaking into the cooling jackets. I guess 2-stroke engines run hot enough for their exhaust manifolds to warrant water-cooling. As a result, I have gaskets in question. When I ran the engine with the t-stat cover off, I had more exhaust coming out of it than I had out the exhaust ports! I changed the head gasket in January. I haven't done a compression check, but I suspect it is fine. I installed it myself, it was installed the correct way, the head and block were clean and smooth, and the bolts were installed with a torque wrench.

The exhaust manifold: I suspect that this is where the leak is located. I'm worried about pulling all those bolts out, since there are lots of them and some may very well get stuck. Then I'll have to drill them out and helicoil what is left.

Any ideas?

Thanx for your help!

T

 

[Chris]

When is the last time you changed the impeller?

That's always where I start. After a few years they just start to disintegrate, so they need to be changed as a regular maintenance item.

-Chris

 

[Tommy in FLL]

I bought the boat from a neighbor last November. He had the bottom end off in his driveway, and he told me that he replaced it then. Boating is his hobby, and from what I can see he seems to know what he is doing. It seems to be pumping fairly well- the "tell-tale" squirts strongly.

Thoughts?

 

[Chris]

Well, what does your neighbour have to say? Did it/he have this issue with it before as well?

If not, I'd be tempted to check the impellar and see what kind of shape it's in and that it was installed properly. I've seen them burn up very quickly from people starting motors dry and I've seen them installed backwards etc.

The other thing that I would try, is flushing the motor really well. Some newer Yamahas have a flush fitting that allows you to hook on a hose and flush the motor without starting it. Your model might not be new enough to have the flush fitting. If that's the case, you can get a flush attachement that looks a little like ear-muffs that allow you to hook a garden hose on to your lower unit. With the muffs, you can flush the system while the motor is running.

-Chris

 

[Tommy in FLL]

Well, what does your neighbour have to say? Did it/he have this issue with it before as well?

If not, I'd be tempted to check the impellar and see what kind of shape it's in and that it was installed properly. I've seen them burn up very quickly from people starting motors dry and I've seen them installed backwards etc.

The other thing that I would try, is flushing the motor really well. Some newer Yamahas have a flush fitting that allows you to hook on a hose and flush the motor without starting it. Your model might not be new enough to have the flush fitting. If that's the case, you can get a flush attachement that looks a little like ear-muffs that allow you to hook a garden hose on to your lower unit. With the muffs, you can flush the system while the motor is running.

-Chris

The story on this boat ['96 Larson/'96 Yamaha] was that it sat in another neighbors' driveway for years. Bob, the man I bought it from, bought it from this guy. The original owner barely used it, and when he did, he apparently never flushed it after use. It's always been used in Ft.Lauderdale's canals- brackish water.

Bob bought the thing, and told me that it overheated on him when he put it in the water and ran it hard. He told me that he replaced the impeller when he got it home, and indeed, the bottom end was off. He later ran it in his driveway with the water muffs you've described and a garden hose, and it appeared to pump fairly well. I made him a way-low offer, and wound up owning it on the cheap = boat, motor, trailer, all in decent shape for $1800. When I got it in the water behind the house, I pulled the plugs and found one of them to be very clean and wet-looking. No smell of gasoline, however- that looked like water to me, and the piston crown looked fairly clean as well. Blown head gasket. We changed out the gasket, and noticed that one of the cylinder barrels was "chipped" on on the water side, so we filled it with Marine-tex and cleaned-off the top of the block. A new gasket went in, and that plug now matches the others.

Yet- there is still exhaust coming from the thermostat housing. Exhaust is getting into the water jackets and causing the sensor to go off. The engine is cool enough after a run that I can put my hand on the t-stat housing, but it is not fouling plugs even without a thermostat. I suspect the gaskets that surround the exhaust manifold, but I've been told so far that I'm likely to break most of the bolts that hold it just trying to remove the cover plate.

Hmmm....

There is a lot of crud in this motor, however. Is there a product or a chemical that can be poured down the channels that will clean this junk out? This motor just runs like a top- it starts on the first click of the key, and when I do open the throttles, it cleanly goes to full power and it has plenty of it too. I'm in a no-wake zone due to all the manatees, and the motor will happily rumble around the neighborhood all day long at 1300 rpm with no problems whatsoever, so it seems like a shame to have to take it down for a few weeks because of some snapped-off bolts.

 

[Chris]

Hi Tommy,

Well it sounds like you got a pretty good deal and knew what you were buying, so investing a little dough is probably justifiable.

The reason I suggested the flush, was because you mentioned the motor had some slime and crud in it. I figured flushing it out might help cure the problem.

Do you have a water temperature guage? If so, does it confirm the motor is overheating? Also, have you checked the ignition system out to see if you've got spark on all cylinders. I ask as you mentioned you've got one wet plug. I know on my Merc, I had a bad switch box and it set off the warning beeper. At first we thought it was an overheat as well, then we discovered the bad switch box and once changed, everything was good to go.

Hopefully you get things figured out.

-Chris

 

[Tommy in FLL]

Hi Tommy,

Well it sounds like you got a pretty good deal and knew what you were buying, so investing a little dough is probably justifiable.

The reason I suggested the flush, was because you mentioned the motor had some slime and crud in it. I figured flushing it out might help cure the problem.

Do you have a water temperature guage? If so, does it confirm the motor is overheating? Also, have you checked the ignition system out to see if you've got spark on all cylinders. I ask as you mentioned you've got one wet plug. I know on my Merc, I had a bad switch box and it set off the warning beeper. At first we thought it was an overheat as well, then we discovered the bad switch box and once changed, everything was good to go.

Hopefully you get things figured out.

-Chris

Hmmm! Well, you know Chris, I haven't actually checked that plug for spark, now that you mention it. The overheat sensor is on top of the engine, and it is a switch that closes at a certain temperature. I bought the SELOC book for this Yamaha motor at the local boating store [there are about 15 here in Fort Liquordale], and it details how to check the sensor. I used my Fluke multi-tester to test the sensor. I put it in a 2.5 quart pot, and put it on the stove, filled with water. I had a thermometer in the water, and the Fluke was set to give a "beep" when continuity had been established. Right on schedule, the sensor went off.

-That spark thing? That really is a good point! I didn't think of that. Chalk one up to you, and if I ever meet you, then you can count on several beers slid your way! I'll check that tomorrow.



T

 

[Chris]

I know on my Merc, the sensors are integrated into the ignition system. So it's therefore not uncommon when you have a ignition issue to get issues with the warning horns or oil alarms etc. A couple years ago, mine was doing exactly what you described. That being, it would run, but once I opened it up, the beeper would start going off. Slow down and it would stop. We tracked it down to a faulty switchbox.

The other thing I would do is a compression test and see what the results are. A leakdown test is another really good indicator as well and is one many people quite often don't do.

Good luck and keep us posted.

-Chris

 

[dave]

running without a thermostst could be causing this problem as well, with no restriction water flow the upper cyclinders on some outboards will be starved for water leaving a hot spot around the temp sensor.